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United States Department of Agriculture

Agricultural Research Service

Title: Fecal strings Associated with Streptococcus agalactiae Infection in Nile Tilapia, Oreochromis niloticus

Authors
item Pasnik, David
item Evans, Joyce
item Klesius, Phillip

Submitted to: The Open Veterinary Science Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2008
Publication Date: January 22, 2009
Repository URL: http://hdl.handle.net/10113/43612
Citation: Pasnik, D.J., Evans, J.J., Klesius, P.H. 2009. Fecal strings associated with Streptococcus agalactiae infection in Nile tilapia, Oreochromis niloticus. The Open Veterinary Science Journal. Volume 3 (6-8).

Interpretive Summary: Nile tilapia (Oreochromis niloticus) were experimentally-infected with Streptococcus agalactiae for several infectivity and vaccine studies. Some of the S. agalactiae-infected tilapia produced considerably longer (up to 20 cm in length) fecal waste strings than historically observed from tilapia at the AAHRL, irrespective of weight or challenge dose. Over time, these fecal strings often became increasingly opaque and white, presumably due to the presence of sloughed mucous cells in the feces or due to the absence of normal fecal matter. Concurrently, the fish also developed overt clinical signs of disease, such as going off feed, depression, exophthalmia, erratic swimming, and death. Samples for bacteriology were obtained from the nares, brain, anterior kidney, and posterior intestines of these fish, and the predominant isolates were identified as S. agalactiae. Control fish from these studies were sham-challenged with tryptic soy broth, and no white, mucoid fecal casts or S. agalactiae isolates were obtained from these fish. This clinical sign of long fecal casts in S. agalactiae-infected fish has not been described. In this group of fish, considerably longer fecal casts were commonly observed in individual fish before other clinical signs appeared. However, acutely affected fish died before the appearance of fecal casts or perhaps these fish failed to eat and therefore did not produce fecal waste. Fecal casts are not frequently examined or emphasized in relation to fish disease, though casts presumably containing sloughed intestinal mucosa and infectious organisms have been observed with a number of viral fish pathogens. The presence of white mucoid fecal casts can be cause for concern and may be a clinical sign of viral or bacterial disease. Fecal clinical analysis and observation could add to the battery of non-invasive diagnostic tests for viral, parasitic, and now bacterial diseases available to the aquatic animal clinician and laboratory technician. Such clinical tests are helpful because they can indicate the early stages of disease, though they may not be useful in acute disease. Fecal casts containing the causative pathogen are also important, because pathogen transmission among fish may be enhanced. Streptococcal infections are known to occur after ingestion of materials containing streptococcal organisms, and the presence of these fecal casts in the tanks may promote S. agalactiae fecal-oral transmission.

Technical Abstract: Nile tilapia (Oreochromis niloticus) were experimentally-infected with Streptococcus agalactiae for several infectivity and vaccine studies. Some of the S. agalactiae-infected tilapia produced considerably longer (up to 20 cm in length) fecal waste strings than historically observed from tilapia at the AAHRL, irrespective of weight or challenge dose. Over time, these fecal strings often became increasingly opaque and white, presumably due to the presence of sloughed mucous cells in the feces or due to the absence of normal fecal matter. Concurrently, the fish also developed overt clinical signs of disease, such as going off feed, depression, exophthalmia, erratic swimming, and death. Samples for bacteriology were obtained from the nares, brain, anterior kidney, and posterior intestines of these fish, and the predominant isolates were identified as S. agalactiae. Control fish from these studies were sham-challenged with tryptic soy broth, and no white, mucoid fecal casts or S. agalactiae isolates were obtained from these fish. This clinical sign of long fecal casts in S. agalactiae-infected fish has not been described. In this group of fish, considerably longer fecal casts were commonly observed in individual fish before other clinical signs appeared. However, acutely affected fish died before the appearance of fecal casts or perhaps these fish failed to eat and therefore did not produce fecal waste. Fecal casts are not frequently examined or emphasized in relation to fish disease, though casts presumably containing sloughed intestinal mucosa and infectious organisms have been observed with a number of viral fish pathogens. The presence of white mucoid fecal casts can be cause for concern and may be a clinical sign of viral or bacterial disease. Fecal clinical analysis and observation could add to the battery of non-invasive diagnostic tests for viral, parasitic, and now bacterial diseases available to the aquatic animal clinician and laboratory technician. Such clinical tests are helpful because they can indicate the early stages of disease, though they may not be useful in acute disease. Fecal casts containing the causative pathogen are also important, because pathogen transmission among fish may be enhanced. Streptococcal infections are known to occur after ingestion of materials containing streptococcal organisms, and the presence of these fecal casts in the tanks may promote S. agalactiae fecal-oral transmission.

Last Modified: 12/21/2014
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